Current project to construct four separate concrete frames with associated substructure works. The most challenging element of the works is the construction of three basements within 5 metres of busy, live rail, viaducts. The most significant is the basement to block ‘C’ which has a footprint of 3500m2 and descends 15m below the newly constructed ground floor slab. This will be constructed using a “top down” methodology to ensure that the Network Rail viaducts are supported at all times.
After construction of the ground floor slab, excavation and construction of the basement will be undertaken through two temporary mole holes constructed within the ground floor slab. Works involve the use of specialist equipment such as Bulk X skips, Chameleon excavators as well as significant ventilation and lighting. Spider cranes within the new basement will assist in the movement and placement of permanent materials.
The two other basements being constructed are using an open dig approach with significant horizontal temporary works schemes to restrict movement of the viaducts.
Concrete frames to each block will progress after completion of the basement, although in the case of block ‘C’ as soon as the ground floor slab is cast. Techniques used in the construction of the frames include post tensioned slabs, slipformed cores, precast concrete columns and walls to improve both programme and quality.
Internal basement drainage will be constructed using cast iron pipework, pumping to high level via 8 pumping chambers. Site wide drainage will also be laid up to 600mm diameter.